(i) Field of the Invention
This invention relates to a sensor array for determining vehicle axles spacings particularly in stop-and-go situations, and more specifically, in situations which are independent of speed. The system can be coupled with various other systems, e.g., weighing, in order to weigh and determine the configuration of the vehicle axles.
(ii) Description of the Prior Art
Axle spacing is important for a number of reasons, but is generally used to classify vehicles into types. For heavy commercial vehicle enforcement, the spacing of axles is important to determine the allowable loads which may be carried by the vehicle. In other applications, the number and spacing of axles is important to determine vehicle fare at toll facilities.
In one type of previous system, a speed detector was combined with an axle detector. The vehicle axle spacings were determined by timing the axle units on the axle sensors, and then, by using the vehicle speed, computing the spacings. In such system, the average vehicle speed was used.
In another system, two axle detectors were used. The speed of each axle was determined, and the speed between two axles was averaged to obtain the overall spacing between two axles, according to the equation: (speed)(time)=distance. In such system, the axle speeds were used.
The axle speed method was more accurate than the vehicle speed method when vehicles were changing speed over the sensors, but neither system worked adequately in a stop-and-go application.
The patent literature also proposed some systems for determining axle spacings. Thus, U.S. Pat. No. 4,539,650 patented Sep. 3, 1985 by T. G. Griffin et al, purported to provide a system for calculating and indicating the weight of moving vehicles. This system was devised particularly for weighing moving vehicles (trucks) on the highway. It included means for sensing both the impact of the mass of the truck, and the speed, each producing an electronic signal, and using the signals to indicate the total weight of the truck. The mass was sensed by an impact component having a bladder, operating on fluid displacement, and producing an electronic signal thereby. The speed was sensed by a radar component, utilizing the Doppler effect, and produced another electronic signal. The two signals determined a signal which indicated the weight of the truck axles. The axles were sensed individually, both as to impact and speed, and the signals produced by these two factors were used as to each axle to show the weight of each axle, and were themselves combined to show the final total weight of the truck. A component was included to sense the presence of the truck in the sensing range, and its departure therefrom, to detect individual trucks following one another and thereby to control the signals relating to each individual truck.
U.S. Pat. No. 4,667,757 patented May 26, 1982 by B. A. Johnson, was said to provide a system for determining the spacing between axles of a vehicle which may be in motion, on the basis of weight alone. A weighbridge was provided with a first load cell spaced from a second load cell along the length of the weighbridge by a specified distance, with each load cell being responsive to the load on its respective location on the weighbridge. After a first axle was on the weighbridge, the weight on the first load cell and the weight on the second load cell were periodically sampled. The average stored weight of the first axle was determined at the time when a second axle was about to enter the weighbridge. The instantaneous weight on the second load cell was measured at the time when the second axle was about to enter the weighbridge. The distance between the first axle and the second axle was determined by calculating. Distances between subsequent axles could also be determined in the following manner: after the first axle had entered the weighbridge at a time when a second axle was about to enter the weighbridge, the weight on the first load cell and the weight on the second load cell were measured and the distance between the first axle and the second axle was determined by calculating, according to the formula: EQU W2L/(W1+W2)